Conventionally, a sealed mixer disclosed in patent document 1 has been, for example, known as the one with a weight for pressing materials inserted into the mixer toward a mixing chamber. Patent document 1 discloses the sealed mixer including a floating weight provided movably upward and downward and capable of pressing materials toward a mixing chamber of a mixer main body, and a shaft member connected to the floating weight and extending in an elevation direction of the floating weight. In such a sealed mixer, lubricant such as grease for easing friction and the like between the floating weight and the shaft member is generally filled in the floating weight.
In the sealed mixer as disclosed in patent document 1, to replace the lubricant in the floating weight and fill the lubricant into the floating weight, an operation of supplying the lubricant into the floating weight has to be performed by opening a hopper door used to supply materials after the floating weight is lifted up to the vicinity of the hopper door and stopped. That is, the lubricant supplying operation can be conventionally performed only after a lifting movement of the shaft member is stopped and it is confirmed that the weight has come to a complete stop. Further, the lubricant supplying operation in a hopper has been very cumbersome.